JPH07295203A - Production of blank for halftone phase shift mask - Google Patents

Abstract

PURPOSE:To obtain a blank for halftone phase shift photomask which is usable for high-resolution lithography having transmittance sufficient to short- wavelength light. CONSTITUTION:This blank for halftone phase shift photomask is obtd. by forming the film of chromium evaporated or sputtered from metal chromium or chromium compd. in plasma formed from a fluorine atom-contg. gas on a transparent substrate 405, thereby forming at least one layer of layers consisting essentially of a chromium fluoride compd on the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for manufacturing high-density integrated circuits such as LSI and VLSI, and particularly for phase shifting for manufacturing a phase-shifting photomask capable of obtaining a fine projected image. The present invention relates to a method for manufacturing a photomask blank.

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are manufactured by repeating a so-called lithographic process using a photomask. Particularly, for forming fine dimensions, for example, Japanese Patent Laid-Open No. 173744/1983. The use of a phase shift photomask as disclosed in the official gazette and Japanese Patent Publication No. 63-59296 is being studied.
Various types of phase shift photomasks have been proposed, and among them, for example, Japanese Patent Application Laid-Open No. 4-136854.
A so-called halftone type phase shift photomask as disclosed in Japanese Patent Publication No. 4890309 and U.S. Pat. No. 4,890,309 attracts attention from the viewpoint of early practical use.
Some proposals have been made regarding a structure and a material capable of improving the yield and reducing the cost by reducing the number of manufacturing steps, such as Japanese Patent Laid-Open Publication No. 5-127361.

A halftone phase shift photomask will be briefly described with reference to the drawings. FIG. 1 is a diagram showing the principle of a halftone phase shift photomask, and FIG. 2 is a diagram showing a conventional method. 1A and 2A are cross-sectional views of the photomask, FIGS. 1B and 2B are amplitudes of light on the photomask, and FIGS. 1C and 2C are Amplitude of light on the wafer, and FIGS. 1D and 2D show light intensity on the wafer, respectively. 101 and 201 are substrates, 202 is 10
A 0% light-shielding film, 102 shifts the phase of incident light by substantially 180 degrees, and a halftone phase shift film having a transmittance of 1 to 50%, and 103 and 203 are incident light. In the conventional method, as shown in FIG. 2A, a 100% light-shielding film 20 made of chromium or the like is formed on a substrate 201 made of quartz glass or the like.
No. 2 is formed to form a light-transmitting portion having a desired pattern, and the light intensity distribution on the wafer widens to the bottom as shown in FIG. 2D, resulting in poor resolution. On the other hand, in the halftone phase shift photomask, the phases of the light transmitted through the halftone phase shift film 102 and the light transmitted through the opening are substantially inverted, so that as shown in FIG. Thus, the light intensity at the pattern boundary becomes 0, and the skirt spread can be suppressed, so that the resolution can be improved.

A point to be noted here is that in a phase shift photomask other than halftone, the light-shielding film and the shifter film have different patterns, and therefore two plate-making steps are required for mask pattern preparation. On the other hand, since the halftone phase shift photomask has one pattern, the platemaking process only needs to be performed once, which is a great advantage of the halftone phase shift photomask.

The halftone phase shift layer 102 of the halftone phase shift mask is required to have two functions of phase inversion and transmittance adjustment. Regarding the phase inversion function, the phase of the exposure light passing through the phase shift portion and the phase of the exposure light passing through the opening may be substantially inverted. Here, the halftone phase shift layer is, for example, M. Bor
n, E. Wolf's "Principles of O"
Since it is treated as an absorption film shown in pp. 628-632 and multiple interference can be ignored, the phase difference φ of the vertically transmitted light is When φ is included in the range of nπ ± π / 3 (n is an odd number), the above-mentioned phase shift effect is obtained.
Here, φ is a phase change that light vertically transmitted through a photomast in which a multilayer film of (m−2) layers is formed on the substrate, and χ ^{k, k + 1} is the kth layer and (k + 1) ) The phase change at the interface with the th layer, u _k and d _k are the refractive index and film thickness of the material forming the k th layer, and λ is the wavelength of the exposure light. However, k = 1 is a mask substrate and k = m is air.

On the other hand, the exposure light transmittance of the halftone phase shift portion for obtaining the halftone phase shift effect is determined by the size, area, arrangement, shape, etc. of the transfer pattern, and differs depending on the pattern. Substantially, in order to obtain the above-mentioned effect, the exposure light transmittance of the halftone phase shift portion should be included within the range of the optimum transmittance ± several% centering on the optimum transmittance determined by the pattern. I have to. Usually, this optimum transmittance is 1 to 50% depending on the transfer pattern when the opening is 100%.
It fluctuates greatly within such a wide range. That is, halftone phase shift photomasks having various transmittances are required in order to deal with all patterns.

In practice, the phase inversion function and the transmittance adjusting function are the complex refractive index (refractive index and extinction coefficient) of the material forming the halftone phase shift film (each material forming each layer in the case of multiple layers). ) And the film thickness. That is, the exposure light transmittance when layered so that the thickness of the halftone phase shift film is adjusted so that the phase difference φ obtained by the equation (1) falls within the range of nπ ± π / 3 (n is an odd number) 1 to 5
A material contained in the range of 0% can be used as the halftone phase shift layer of the halftone phase shift photomask. As such a material, for example, Japanese Patent Laid-Open No. 5-1
A film containing a chromium compound as a main component, which is disclosed in Japanese Patent No. 27361, is known.

The film containing a chromium compound as a main component is an oxide, a nitride, an oxynitride, an oxycarbide, or an oxycarbonitride of chromium. The transmittance of these films with respect to the exposure light is the wavelength of the exposure light. Depends on For example, FIG. 3 shows a spectral transmittance curve of a chromium oxide film formed on a synthetic quartz substrate by a reactive sputtering method in an oxygen atmosphere using a chromium target. Here, the thickness of the chromium oxide film is about 50 nm. As is clear from FIG. 3, the transmittance of the chromium oxide film drops sharply in the short wavelength region. Therefore, a halftone phase shift photomask using this chromium oxide in the halftone phase shifter layer is used for a g-line (436 nm) and an i-line (365 nm) of a high pressure mercury lamp.
Although it can be used for high-resolution exposure, a krypton excimer laser fluoride (248n
In the case of exposure with deep ultraviolet rays such as m), the transmittance is too low,
There was a problem that it could not be used. In addition, since chromium nitride film, chromium oxynitride film, chromium oxycarbide nitride film, and chromium oxycarbonitride film cannot be used for deep UV exposure such as krypton fluoride excimer laser, there is a problem that they cannot be applied to high resolution lithography. there were. Further, the chromium compound film containing a fluorine atom,
Since the optical constant is determined by the fluorine content, it is important to adjust the composition of the chromium compound film in order to obtain an accurate mask, but with the conventional reactive sputtering method, the composition of the film is It was difficult to control precisely.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances and has a sufficient transmittance for short wavelength light and is exposed to deep ultraviolet rays such as a krypton fluoride excimer laser. A halftone phase shift photomask usable for high resolution lithography and a blank for a halftone phase shift photomask.

[0010]

In view of the above problems, the present invention has a transmittance of halftone phase when a film is formed to a film thickness that reverses the phase of far ultraviolet light such as krypton fluoride excimer laser. The research was completed as a result of research to develop a manufacturing method of a halftone phase shift material included in a range usable as a shift layer. That is,
The present invention relates to a method for producing a blank for a halftone phase shift photomask, which comprises at least one layer mainly containing a chromium compound containing a fluorine atom as the halftone phase shift layer. A film mainly composed of a chromium compound containing a fluorine atom transmits light in a short wavelength range as compared with a conventional film mainly composed of chromium oxide, chromium nitride, chromium oxynitride, chromium oxycarbide, or chromium oxycarbonitride that does not contain a fluorine atom. Due to its excellent rate, it is possible to obtain a transmittance that can be sufficiently used as a halftone phase shifter film, even if a film is formed on a transparent substrate with a film thickness that reverses the phase of far ultraviolet light such as krypton excimer laser. Become.

In the halftone phase shift lithography, the refractive index and the extinction coefficient of the film forming the halftone phase shift layer with exposure light are obtained by, for example, ellipsometry, and the exposure is calculated by the above equation (1). It is required that the transmittance when the film thickness required to invert the phase of light is formed on the transparent substrate is the optimum transmittance determined from the transfer pattern and the like. Assuming krypton fluoride excimer laser exposure, the conventional film mainly composed of chromium oxide, chromium nitride, chromium oxynitride, chromium oxycarbide, and chromium oxycarbonitride that does not contain fluorine atoms has a film thickness that causes phase inversion. The transmittance of the compound is too low to be used as a halftone phase shift layer, whereas the chromium compound containing a fluorine atom of the present invention varies in refractive index and extinction coefficient depending on the ratio of the fluorine atom and other atoms contained. ,
The transmittance for the exposure light at the film thickness when the phase is inverted is
The composition can be adjusted to obtain the required optimum transmittance. In this case, a single layer can be used as a halftone phase shift layer, but within a range that does not impair the phase inversion function after the film is formed so that the transmittance for exposure light is higher than the required transmittance. It is also possible to stack a light shielding layer for adjusting the transmittance.

By the way, since the optical constant of the chromium compound film containing a fluorine atom is determined by the content ratio of fluorine or the like as described above, in order to obtain an accurate halftone phase shift photomask, the composition of the film is required. It is important to control precisely. In addition, a stoichiometrically stable compound rarely satisfies both the phase inversion function and the transmittance adjusting function, and it is generally required to form an intermediate compound film. The present invention relates to a production method for forming a film of these intermediate compounds with a desired composition with high precision. That is, in the method for producing a chromium compound containing a fluorine atom of the present invention, in a thin film forming method of evaporating chromium in a vacuum chamber and depositing it on a transparent substrate for a photomask, the evaporated chromium is deposited on the substrate. This is a production method of reacting with a fluorine atom before, and in particular, the reaction between chromium and a fluorine atom is carried out by passing evaporated chromium through plasma of a gas containing a fluorine atom. Here, the chromium evaporation source may be either pure metal chromium or a chromium compound, and as means for evaporating these, irradiation of accelerated electrons by an electron gun, ion irradiation by an ion gun, etc. are preferable, but a coil, a boat, etc. are used. Resistance heating can also be used. Further, as a means for generating the above-mentioned plasma, a high frequency electric field of capacitive coupling or inductive coupling may be applied to a space into which a gas containing a fluorine atom is introduced in advance, or plasma may be generated by a direct current electric field. Further, it is possible to introduce a gas ionized by an ion gun into the space in which the gas containing the fluorine atom is introduced, or to ionize the gas containing the fluorine atom itself by the ion gun and then introduce the gas into the space. .
Further, as the gas containing a fluorine atom, fluorine, a carbon fluoride gas, sulfur hexafluoride, nitrogen trifluoride, chlorine trifluoride, or the like can be used.

Further, chromium particles are generated by sputtering from a chromium target, and plasma generated from a fluorine atom-containing gas is generated by an ion gun, so that a fluorine compound-containing chromium compound film having a desired composition and a uniform film thickness is obtained. Can be formed. In order to control the optical constants of the compound film formed by this film forming method, the reaction in the plasma space described above may be controlled, and the amount of chromium to be evaporated, the flow rate of the fluorine atom-containing gas, the pressure, the plasma The power applied for generation may be controlled. In addition, the characteristics of the apparatus used such as the shape of the reaction space and the method of introducing the gas also affect the optical characteristics of the film to be formed, so it is preferable to arbitrarily set in consideration of these and to heat the substrate to be evaporated. You may.

The above-described method for producing a chromium compound containing a fluorine atom can accurately realize a desired composition even in an intermediate state which is not stoichiometrically stable, so that a halftone phase shift film having various optical constants can be obtained. Can form a film.
In addition, the residual stress of the film is reduced, and a film having improved adhesion to the substrate can be easily obtained. Further, the deposition rate is practically sufficient. Further, although the single layer film of the chromium fluoride compound has been described above, the same can be applied to the case where the halftone phase shift layer has a multilayer structure.

Further, when the chromium compound containing a fluorine atom formed by the manufacturing method of the present invention is used as a single layer in the halftone phase shift layer, the chromium atom of the conventional photomask is used because the chromium atom is the base material. Patterning can be performed in almost the same way as the light-shielding film. Even in the case of a multilayer film, when chromium, chromium oxide, chromium nitride, chromium oxynitride, chromium oxycarbide, chromium oxycarbonitride, or the like is used as the light-shielding film, one patterning step is performed by almost the same method as the conventional method. You can make a plate with. Therefore, yield improvement and cost reduction can be realized.

[0016]

The method of manufacturing a blank for a halftone phase shift photomask of the present invention can provide a blank for a halftone phase shift photomask which can be used for far-ultraviolet exposure such as a krypton fluoride excimer laser. Resolution lithography can be realized. Further, since the blanks can be masked by almost the same method as the conventional photomask, the yield can be improved and the cost can be reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a blank for a halftone phase shift mask of the present invention will be described below with reference to the drawings.
FIG. 4 is a diagram illustrating an example of an apparatus used for manufacturing blanks for a halftone phase shift photomask of the present invention. In FIG. 4, the vacuum chamber 401 is connected to an exhaust device and a waste gas treatment device through a butterfly valve 402. A chromium evaporation source 40 is provided in the vacuum chamber 401.
3, an electron gun 404, and a photomask substrate 405 are arranged. Further, 406 is a reactive gas supply port, and 407 is a high frequency current supply coil. Butterfly valve 402
After evacuating the inside of the vacuum chamber 401 to a predetermined degree of vacuum, the mass flow controller 408 adjusts the flow rate to introduce carbon tetrafluoride gas into the vacuum chamber through the supply port 406. Next, by adjusting the butterfly valve 402, the pressure in the vacuum chamber is adjusted to a vacuum degree suitable for plasma generation, a high-frequency current is applied to the coil 407, and plasma is generated in the space between the substrate 405 and the evaporation source 403. Then, accelerated electrons are emitted from the electron gun 404 to the chromium evaporation source 403 made of pure metal chromium to start evaporation of chromium. After the electron emission state and the plasma discharge state have stabilized, the shutter 409 covering the substrate 405 is opened and film formation is started to form a film having a predetermined film thickness.

FIG. 5 is a view for explaining another example of an apparatus used in the method for manufacturing blanks for a halftone phase shift photomask of the present invention. The vacuum chamber 501 has the same structure as the vacuum chamber 401 shown in FIG.
Is installed. This ion gun ionizes the gas supplied into the tank through the carrier gas inlet 507 to generate plasma of the carrier gas in the space between the chromium evaporation source 503 and the photomask substrate 505, and further the chromium evaporation source 503. Is irradiated to evaporate chromium. To manufacture photoblanks for a halftone phase shift photomask with this apparatus, the butterfly valve 502 is opened, the inside of the vacuum chamber 501 is evacuated to a predetermined degree of vacuum, and then argon is introduced into the vacuum chamber while adjusting the flow rate with the mass flow controller 510. And the butterfly valve 5
02 is adjusted so that the pressure is suitable for plasma generation. Next, an electric current is applied to the filament in the ion gun and a voltage is applied to the ion flow extraction electrode to ionize the argon passing through the ion gun to generate argon plasma in the vacuum chamber. Reference numeral 511 is a focusing coil for controlling the spread of plasma. Next, the mass flow controller 508 adjusts the flow rate to supply carbon tetrafluoride from the gas supply port 506 into the vacuum chamber. When the plasma becomes stable, the shutter 509 is opened to start film formation on the substrate.

FIG. 6 is a view for explaining another apparatus used in the method for manufacturing blanks for a halftone phase shift photomask of the present invention. The vacuum chamber 601 has the same configuration as the vacuum chamber 401 shown in FIG. 4, but is equipped with an ion gun 604. This ion gun has a carrier gas inlet 60
The gas supplied into the chamber from 7 is ionized to generate a carrier gas plasma in the space between the chromium target 603 and the photomask substrate 605. Further, the mass flow controller 608 adjusts the flow rate in the same manner as in FIG. 5, and supplies the fluorine atom-containing gas from the gas supply port 606 into the vacuum chamber. Chrome target 603 and photomask substrate 605
A high-frequency voltage or a direct-current voltage is applied from a power source 612 to generate chromium particles by sputtering and react with plasma of a fluorine atom-containing gas to form a fluorine atom-containing chromium compound on the photomask substrate.

Example 1 A photoblank for a halftone phase shift photomask was manufactured using the apparatus shown in FIG. Open the butterfly valve 402 and move the inside of the vacuum chamber 401 to 1 × 10 ⁻⁵ Tor.
After exhausting up to r units, mass flow controller 408
A carbon tetrafluoride gas whose flow rate is controlled to 100 sccm is introduced into the vacuum chamber through the supply port 406. Next, by adjusting the butterfly valve 402, the pressure in the vacuum chamber is set to 5 × 10 ⁻³ Torr, and the coil 407
A high-frequency current of 150 W (13.56 MHz) is applied to generate a plasma in the space between the substrate 405 and the evaporation source 403, and subsequently, an accelerated electron is emitted from the electron gun 404 into a chromium evaporation source 403 made of pure metal chromium. Then, the evaporation of chromium is started. After the electron emission state and the plasma discharge state are stabilized, the shutter 409 covering the substrate 405 is opened and film formation is started. At this time, when the film formation rate was monitored by the crystal oscillator film thickness monitor, it was 0.5 n / s.
It was m. Under this condition, about 50n on a silicon wafer
KrF excimer laser wavelength (248n
The optical constant at m) was determined by ellipsometry, and u
= 1.723 and k = 0.2255. This is the same as that in the text. Born, E. Wolf "Pri
nciples of Optics "628-632
When the film was treated as a metal film shown on the page and formed on a photomask substrate, the film thickness required to shift the phase of transmitted light of 248 nm by 180 degrees was calculated to be 170 nm.

Further, the obtained fluorine atom-containing chromium compound film was subjected to X-ray electron spectroscopy (VG SCIENTIFIC).
The atomic ratio of chromium to fluorine was 1: 4, as measured by ESCALAB210). Approximately 170 n of a chromium compound film containing a fluorine atom is formed on a highly purified quartz substrate that has been optically polished and well washed under the same conditions as above.
The transmittance when a film is formed is as shown in FIG. The transmittance at 248 nm at this time is 10.5%.
Is. This halftone phase shift photomask blank can be masked by almost the same method as a conventional photomask, and is processed into a good halftone phase shift photomask for KrF excimer laser exposure.

Example 2 A halftone phase shift photomask blank of the present invention was manufactured by the apparatus shown in FIG. Open the butterfly valve 502 and move the vacuum chamber 501 to 1 × 10 ⁻⁵ To.
After exhausting to rr stand, mass flow controller 51
Argon whose flow rate is controlled to 50 sccm by 0 is supplied into the vacuum chamber. Here, after adjusting the butterfly valve 502 to a pressure of 5 × 10 ⁻³ Torr, an electric current is passed through the filament in the ion gun and a voltage is applied to the ion flow extraction electrode, so that the argon passing through the ion gun is passed through. Is ionized to generate argon plasma in the vacuum chamber. Reference numeral 511 is a focusing coil for controlling the spread of plasma. Next, mass flow controller 508
The carbon tetrafluoride whose flow rate is controlled to 50 sccm is supplied from the gas supply port 506 into the vacuum chamber. When the plasma becomes stable, the shutter 509 is opened to start film formation on the substrate. The chromium compound film containing a fluorine atom formed by this method showed almost the same characteristics as the film formed in Example 1 and was a good shifter for a halftone phase shift photomask.

[0023]

According to the method of manufacturing a blank for a halftone phase shift photomask of the present invention, it is possible to obtain a blank for a halftone phase shift photomask which can be used for far-ultraviolet exposure such as a krypton fluoride excimer laser having a short wavelength. As a result, high resolution lithography can be realized, and the blanks can be masked by almost the same method as the conventional photomask, so that the yield can be improved.
Cost reduction can be realized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a halftone phase shift photomask.

FIG. 2 is a diagram illustrating a conventional phase shift photomask.

FIG. 3 is a diagram illustrating the transmittance of a chromium oxide film formed on a synthetic quartz substrate by reactive sputtering in a oxygen atmosphere using a chromium target.

FIG. 4 is a diagram illustrating an example of an apparatus used in the method for manufacturing blanks for a halftone phase shift photomask of the present invention.

FIG. 5 is a diagram illustrating another example of an apparatus used in the method for manufacturing blanks for a halftone phase shift photomask of the present invention.

FIG. 6 is a diagram illustrating another embodiment of the apparatus used in the method for manufacturing blanks for a halftone phase shift photomask of the present invention.

FIG. 7 is a diagram for explaining the transmittance when a chromium compound film containing fluorine atoms is formed to a thickness of about 170 nm on a high-purity quartz substrate.

[Explanation of symbols]

401 ... Vacuum tank, 402 ... Butterfly valve, 403 ...
Chromium evaporation source, 404 ... Electron gun, 405 ... Photomask substrate, 406 ... Reactive gas supply port, 407 ... High frequency current supply coil, 408 ... Mass flow controller, 4
09 ... Shutter, 501 ... Vacuum chamber, 502 ... Butterfly valve, 503 ... Chromium evaporation source, 504 ... Ion gun,
505 ... Photomask substrate, 506 ... Gas supply port, 5
07 ... Carrier gas inlet, 508 ... Mass flow controller, 509 ... Shutter, 510 ... Mass flow controller, 511 ... Focusing coil, 601 ... Vacuum chamber,
603 ... Chrome target, 604 ... Ion gun, 605
... Photomask substrate, 606 ... Gas supply port, 607 ...
Carrier gas inlet, 608 ... Mass flow controller, 609 ... Shutter, 610 ... Mass flow controller, 611 ... Converging coil, 612 ... Power supply

Claims (7)

[Claims] 1. A method of manufacturing a blank for a halftone phase shift photomask, wherein a chromium fluoride compound is deposited on a transparent substrate by evaporating or sputtering chromium from metallic chromium or a chromium compound in a plasma generated from a gas containing a fluorine atom. A method for producing a blank for a halftone phase shift photomask, which comprises forming a layer mainly comprising 2. A chromium evaporation method of manufacturing a halftone phase shift photomask blank according to claim 1, characterized in that the irradiation of electron irradiation or ionizing gas accelerated by the electron gun. 3. A fluorine atom plasma generated from containing gas according to claim 1 or 2, characterized in that generated by spatial ionized while introducing a fluorine atom-containing gas between the chromium source and the transparent substrate A method for manufacturing a blank for a halftone phase shift photomask according to any one of 1. The plasma generated from 4. fluorine atom-containing gas, according to claim 1, characterized in previously ionized to thus be generated in the introduction of fluorine atom-containing gas into a space between the chromium source and the transparent substrate or 3. The method for manufacturing a blank for a halftone phase shift photomask according to any one of 2 above. 5. A plasma generated from a fluorine atom-containing gas is generated by introducing a gas atomized in advance while introducing the fluorine atom-containing gas into the space between the chromium source and the transparent substrate. A method for manufacturing a blank for a halftone phase shift photomask according to claim 1. 6. A fluorine atom-containing gas which has been ionized in advance is irradiated to the chromium source through a space between the chromium source and the transparent substrate to evaporate chromium and to generate plasma containing fluorine atoms, thereby producing a transparent film. The method for manufacturing a blank for a halftone phase shift photomask according to claim 1, wherein a layer mainly containing a chromium fluoride compound is formed on the substrate. 7.